A short introduction to RDMA | isomerica.net

RDMA - Remote DMA - extends DMA concept to networking. Networking tends to involve a lot of data copying, and a lot of work by the operating system. Many network cards support DMA already, but this only allows a DMA transfer of raw network data from the card into the OS Kernel’s memory. This data must be decoded as it moves through the protocol stack, which typically involves additional copying, and eventually it is deliver to a user space program (which involves yet another copy). All this copying is particularly necessary since the kernel must virtualize the shared network interface to all the programs running on a system. The kernel needs to ensure that a user program cannot read network traffic meant for a different program. As network interfaces keep getting faster this overhead becomes more and more significant. Special network interface cards implement the protocol stack in silicon on the card.

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